A trilogy goes to new lengths : SO LONG, AND THANKS FOR ALL THE FISH by Douglas Adams (Harmony: $12.95: 224 pp.)

Douglas Adams is a . . . NUT. And not of the macadamian variety. Not satisfied with a reputation that has become a byword in science fiction (a word not mentionable in polite society) or for creating a rush on hotel towels--and oh, yes, “The Hitchhiker’s Guide to the Galaxy,” a must for those extra-terrestrial minded. No-ooo --he has to go write yet a fourth book in his aforementioned trilogy and extend his reputation (and career) even further.

When last we dealt with the peripatetic Arthur Dent (Our Hero) in “Life, the Universe and Everything,” he was left with the information that on a certain planet was God’s Last Message to His Creation. The message is NOT the title to the book--that’s a message from someone else and only good ol’ Wonko the Sane of California knows just from whom and to whom it is. And just what it has to do with the rest of the story.

Arthur Dent returns to Earth, to his favorite village pub, confused but glad to be here, since as last he knew, the planet had been previously destroyed by the Vogons to make way for an inter-galactic freeway.

Things get more complicated. Dent meets the girl of his dreams, Fenchurch. He gets his job back with the BBC. Ford Prefect has been trying to ring him for simply ages . He learns how to fly without the aid of a plane or glider, and--all the dolphins have disappeared, but they have left a clue behind. Dent and Fenchurch have an important voyage to make, to read God’s Last Message, etc. etc. and well, that would be telling. . . .

There is much more wonderful, inventive, totally Douglas Adams humor let loose between the innocent pages of this book in his wild, whiplash style and short chapters. I must give you an example, from the “Guide’s” entry on San Francisco, we find: “A good place to go. It’s very easy to believe that everyone you meet there is also a space traveler. Starting a new religion for you is just their way of saying ‘hi.’ Until you’ve settled in and got the hang of the place it is best to say ‘no’ to three questions out of any given four that anyone may ask you. . .”

I, for one, am grateful that we haven’t seen the end of Arthur Dent (or the universe for that matter), and I sincerely hope that there is even a fifth book in the “Hitchhiker’s Guide to the Galaxy” trilogy.